Such a reactor is described in U.S. Pat. No. 5,449,498. According to this publication the lower end of the primary cyclone is provided with an opening to allow stripping gas and stripped hydrocarbons as discharged upwardly from the stripping zone to enter the primary cyclone from below. Special measures are needed at this opening connecting the primary cyclone and the stripping zone to ensure that catalyst particles can flow downwards and striping gas and stripped hydrocarbons can flow upwards into the primary cyclone.
A disadvantage of this reactor is that the separation in the primary cyclone can be negatively influenced when level fluctuations may for example be caused by pressure fluctuations in the system, by standpipe-instabilities or slide-valve problems.